The present invention pertains to a live steam (high temperature/pressure steam) passage that is movable under the effect of heat between the inner housing and the outer housing of a steam turbine via a piston ring connection.
In steam turbines which are designed for higher pressures and/or temperatures, the so-called double-shell design is used, in which an inner housing is mounted within the outer housing. In this design, there are temperature and pressure gradients from the inside to the outside, as a result of which the load on the individual housing parts is limited in accordance with such gradients.
Because the expansion and the shrinkage of the outer housing and the inner housing are different during the different phases of operation, it is necessary to make the steam-tight connection between the two housing parts elastic.
Consequently, it is known that in steam turbines, the steam being admitted can be sent directly into the inner housing by means of a sealed passage through the outer housing, and the steam first performs its work of expansion in the inner housing. In this design, the outer housing comes into contact only with the steam being discharged from the inner housing.
Consequently, designs with an inner housing in steam turbines belong to the state of the art, and they are conventionally designed as L-ring or angle ring connections, I-ring connections, or piston ring connections.
Angle ring connections have the disadvantage that their manufacture is complicated and expensive, because double seating surfaces with high accuracy of fit must be prepared on both the ring and the annular seats.
A disadvantage of the I-ring connection is the fact that the ring is unable to accommodate any relative movements in its plane. Therefore, it can be used only with limitations.
Piston ring connections have been used so far in two different designs:
As a loose double piston ring sleeve, which carries piston rings on each side, by means of which it must seal in both the outer housing and the inner housing of the turbine. This implies the risk of additional leaks.
Single piston ring seal design, which seals only in the inner housing, while the piston rings sit on an inlet a nozzle element or connection piece welded rigidly to the outer housing, is problematic in terms of manufacture, because the piston ring grooves can be prepared only after the inlet connection piece has been welded in during the machining of the housing halves of the turbine. This may require special tools for reasons of accessibility, especially in the case of smaller turbines with smaller housing diameters.